The cytokine-activated tyrosine kinase JAK2 activates Raf-1 in a p21ras-dependent manner

Proc Natl Acad Sci U S A. 1996 Oct 15;93(21):11681-6. doi: 10.1073/pnas.93.21.11681.


JAK2, a member of the Janus kinase superfamily was found to interact functionally with Raf-1, a central component of the ras/mitogen-activated protein kinase signal transduction pathway. Interferon-gamma and several other cytokines that are known to activate JAK2 kinase were also found to stimulate Raf-1 kinase activity toward MEK-1 in mammalian cells. In the baculovirus coexpression system, Raf-1 was activated by JAK2 in the presence of p21ras. Under these conditions, a ternary complex of p21ras, JAK2, and Raf-1 was observed. In contrast, in the absence of p21ras, coexpression of JAK2 and Raf-1 resulted in an overall decrease in the Raf-1 kinase activity. In addition, JAK2 phosphorylated Raf-1 at sites different from those phosphorylated by pp60v-src. In mammalian cells treated with either erythropoietin or interferon-gamma, a small fraction of Raf-1 coimmunoprecipitated with JAK2 in lysates of cells in which JAK2 was activated as judged by its state of tyrosine phosphorylation. Taken together, these data suggest that JAK2 and p21ras cooperate to activate Raf-1.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism
  • Cell Line
  • Cytokines / pharmacology*
  • Enzyme Activation
  • Erythropoietin / pharmacology
  • Granulocyte-Macrophage Colony-Stimulating Factor / pharmacology
  • HeLa Cells
  • Humans
  • Interferon-gamma / pharmacology
  • Interleukin-2 / pharmacology
  • Janus Kinase 2
  • MAP Kinase Kinase 1
  • Mitogen-Activated Protein Kinase Kinases*
  • Protein Serine-Threonine Kinases / isolation & purification
  • Protein Serine-Threonine Kinases / metabolism*
  • Protein-Tyrosine Kinases / isolation & purification
  • Protein-Tyrosine Kinases / metabolism*
  • Proto-Oncogene Proteins / isolation & purification
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-raf
  • Proto-Oncogene Proteins p21(ras) / isolation & purification
  • Proto-Oncogene Proteins p21(ras) / metabolism*
  • Recombinant Proteins / pharmacology
  • Signal Transduction
  • Spodoptera
  • Transfection


  • Cytokines
  • Interleukin-2
  • Proto-Oncogene Proteins
  • Recombinant Proteins
  • Erythropoietin
  • Interferon-gamma
  • Granulocyte-Macrophage Colony-Stimulating Factor
  • Protein-Tyrosine Kinases
  • JAK2 protein, human
  • Janus Kinase 2
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-raf
  • Calcium-Calmodulin-Dependent Protein Kinases
  • MAP Kinase Kinase 1
  • MAP2K1 protein, human
  • Mitogen-Activated Protein Kinase Kinases
  • HRAS protein, human
  • Proto-Oncogene Proteins p21(ras)